The invention deals with a knock-out instrument for the shanks of hipjoint prostheses, consisting of a shank with a coupling-part for a sliding hammer as well as of an extension-piece which may be applied in the knock-out direction.
Knocking out the shanks of hipjoint prosthesis is unavoidable in the case of secondary operations in order to prepare the bed in the bone for a new shank. The shanks of prostheses therefore often exhibit holes or tapped holes in the proximal part of the shank of the prosthesis, to which an extractor tool may be applied which is connected via coupling-part to a hammer in such away that the shank is extracted by blows in the direction of extraction because of the inertia of the bone concerned. A knock-out instrument of that kind is shown in the EP 0 244 610. In that case a hook ending as a finger engages in a drilled hole which lies transversely to the axis of the shank of the prosthesis. One disadvantage of the executions hitherto is that holes or possibilities of coupling must be provided on the shank of the prosthesis, which become obstructed by body tissues and depend for their accessibility upon a shank projecting from the prosthesis in the direction of extraction, possibly weaken the prosthesis and in the case of cement-free anchoring reduce the possible area of engagement for a knock-in tool.